It is well known that power can be wirelessly conveyed from one place to another using the Faraday effect, whereby a changing magnetic field causes an electrical current to flow in an electrically isolated secondary circuit. Magnetic inductive charging is the most popular form of wireless power transfer currently in use. The basic form of magnetic inductive charging uses two coils in close proximity where one coil acts as the wireless power transmitter and the other acts as the receiver of wireless power. A time-varying current flows in the transmitter coil, which produces a time-varying magnetic field. This time-varying magnetic field induces current in the nearby receiver coil (Faraday's law), which can then be used to charge various devices.
Magnetic-coupling technology has also been described as a viable wireless power transfer solution. The technology may make use of a strong magnetic coupling whereby a rotating magnet in a wireless power transmitter couples onto another nearby magnet in the wireless power receiver. The transfer of energy is via rotational magnetic coupling rather than direct magnetic induction mechanism. The time-varying magnetic field generated by the rotating magnets typically has a lower frequency compared to magnetic induction systems.
There are health and safety concerns of stray magnetic fields in wireless power transfer systems. Additionally, stray magnetic fields also induce eddy currents in nearby metallic objects creating heat which results in a loss of power transfer efficiency.